The present invention relates to the field of adjustable shims, used most commonly in the construction industry, for spacing window or door frame units in the rough openings formed of lumber in a wall. The following United States patents disclose various arrangements for accomplishing such a result: U.S. Pat. Nos. 2,169,985, 2,651,814, 2,753,602, 2,997,750, 3,345,780, 3,614,846, 3,654,734, 4,014,146. None of these devices, however, provide a simple, inexpensive, two-piece unit which provides for incremental adjustment of the spacing without the use of tools other than a forceexerting member such as a hammer or block of wood.